Separation of ethane and ethylene by extractive distillation



Patented Sept. 16 1952 SEPARATIONHOF ETHANE AYNDLETHYLENE BY EXTRACTIVE DISTILLATION John A. Patterson, Beverly, N.f J.', assignor to Standard Oil Developmentcompany, a co rpo ration of Delaware Application July a, 1947, Serial No. 758,841

This invention relates to the separation of low molecular weight unsaturated hydrocarbons from gaseous mixtures containing the low molecular Weight hydrocarbons and in particular, to the separation of ethylene from hydrogen and methane as constituents of refinery gases.

The separation of ethylene from refinery gases has become important for the use of the compound as a chemical intermediate in the preparation of chemicals containing the ethyl and substituted ethyl groups. Prior art processing for the separation of ethylene from hydrogen and methane usually involves considerable refrigeration when a high recovery of ethylene is desired. Also, ammoniacal copper solutions have been used for separating the ethylene from such mixtures. In the present invention, ethylene is removed from association with hydrogen and methane and by treating the mixture especially in a distillation zone with a liquid polar solvent alone or in admixture with Water.

Processing according to the invention involves subjecting the low molecular weight hydrocarbon gaseous mixtures to the action of a polar, preferably water soluble, solvent, liquid at the, temperature of the treatment, to depress the volatility in a distillation zone of ethylene relative to hydrogen and methane. Thus the invention involves treating the low molecular weight hydrocarbon mixture to an extractive distillation in the presence preferably of a non-hydrocarbon polar solvent. In such processing, the solvent is admitted into a distillation zone either with reflux or upon one of the higher plates so that the distillation vapors are counterourrently contacted with the liquid solvent. In this treatment the effects of temperature and pressure have been found to be interrelated. The processing may be conducted at normal temperatures and under pressures of the order 01 500 pounds gauge and higher, but preferably temperatures of between and 120 F. and pressures from 200 to 300 pounds per'square inch are employed. The higher pressures areemployed particularly when products in the liquid form are desired. The absorbed gas may be recovered by heating or reducing the pressure of the solution or the solution may be used directly as the source of ethylene. The solvent may be readily separated from the solution by stripping at lower pressure and/or at higher temperatures.

5 Claims. (Cl. 183-115).

In order that the invention may be thoroughly understood, the following description and illustration of processing of a refinery gas containing mainly hydrogen, methane, ethylene and ethane may be taken. A typical refinery gas mixture subsequent to a preliminary distillation has the following composition; 1 4

Per cent Hydrogen 19.3 Methane 33.2 Ethylene 34.3 Ethane 13.0 Propylene 0.2

I Usually the preliminary distillation is effected upon a mixture of this type in order-to obtain a more concentrated C2 fraction and remove the bulk of the heavier material. In the description the reference numerals refer to the accompanying drawing in which the flowof-materials is indicated through asuitable form of processing equipment. I

The feed supply is passed through line I I at a temperature of F. andpressure of 250 pounds gauge to the distillation equipment, usually a baflie tray tower in. In order that the feed may have the temperature and pressure as given, passage of the gaseous mixture through pressuring and heat exchange equipment not shown prior to its passage into theline l-l ismade. The tower I0 is equipped with an overhead vapor line I2, a

I condenser l3, a drum H, a reflux line I5, adistillate withdrawal line IS. a bottoms withdrawal line H, and a solvent line 29. 'The tower [0 usually contains about plates. The feed supply passed through line H enters the tower In on about the 20th plate. The heat is supplied to the tower ID by means of closed steam coil or the sensible heat of the solvent recycle to the tower as a result of passing a portion of the solution withdrawn through line ll to the reboiler IS in which a portion is vaporizedby the recycled pressure.

Per cent Hydrogen 36.6 Methane 63.0 Ethylene .4 Ethane Trace This material is passed through the condenser l3 and is cooled to a temperature of 5 F. in order to recover by condensationany vaporized solvent;

The condensate is returned to the top of the tower through line l5. The uncondensed portion is passed through line 16 and. removed? from the system. The liquid removed through line I! contains the ethylene admixed with solvent in the ratio of 20 pounds of solvent per pound of hydrocarbon. The portion of the stream not passed through the reboiler I8 is withdrawn through line 2| and through the flash drum 24 where the pressure is reduced to Spoundsper square inch. Most of the ethylene content: is "vaporized and is removed from the drum through -line:28, for;subsequent treatment. The 'unvaporized; portion of the extract stream consisting of". the acetone-*- water solvent containing some ethyleneiswithdrawn from drum 24 and-introduced'intothe J stripper tower 20 by line 25.

' Tower 2 0 is shown asan example of distillation of usual construction containing 2 0"b'ubble1 cap plates. It isprovided'with-a-vapor line22; a partialcondenser 2 3; a bottoms withdrawal line 2 1,

' and a reboiler 28. The tower-20 isjused to, strip refrigerated. cooler I9, and-tothe tower 10.

The overhead vapor from the tower: 20:which consists of ethylene and someacetoneandwater is removed throughline 22 .to-the; partial .condenser- 23 where the :major partof; the; acetone and water is1condensed. The;mixture.;is.conducted to the flash drum 24 .previously:described where theliquid solvent,andvaporethylene are separated. The ethylene in the vaporphasecontains a small amount of solventdue,toitsipartial This mixture is, conducted. through line 26 to the extraction equipment 30.

Equipment-30 is shown asbeingzaicounterdistillation for the removal of the-ethane and propylene, .a purity of 95% is readily obtainable.

,The dilute solution of acetone is withdrawn through line for recoveryof-its acetone content in equipment not shown.

In the invention, the polar solvents which may be most advantageousl used are any of the lower molecular weight liquid oxygenated hydrocarbons such as the alcohols, ethers and ketones alone or in admixture with water. In using these solvents, the amount of solvent circulation and the transfer of heat is reduced to a minimum. Also, the need for low subatmospheric temperatures is obviated and solvent lost in the overhead gas is minimized. A particular advantage in the use of the preferable solvents in this invention is that if subatmospheric temperatures are necessary, the need for drying the feed gas is either unnecessary or can be efiected by preliminary scrubbing with the solvent itself. In

this connection acetone, iurtural and their :a'queou's-"solutions are particularly desirable solvents for use in this invention. When the solvent employed is hydrocarbon in character, the convenience of nearby sources of ethane, C3, C4, C5 and as high as Ca hydrocarbon streams from cracking and other petroleum refinery operations ethane'from af gaseous mixture. containing hydrogen,' methane,'ethylene and ethane which comprises'subjecting the gaseous mixture to extractive distillationat a pressureof 200 to 300 p. s; i. in an extractive distillation zone in-the presence .of'a 'solventselected from'the group consisting of acetone, furfural and, water solutions thereof, whereby..ethylene and, ethane are absorbed by the. solvent, removing ar'dis'tillate containinghydm enand methanejfrom the distillation zone, and removing .a solution of 3. A process according to claim 1. in which 'the solvent is furfural.

, 4. A process according to claimv 1 in whichv the solvent is acetone.

5. A process according to claim 1 wherein the ethylene and ethaneare recovered from solution in the, solventjby. reducing the pressure .on the solution whereby a portion of the ethylene ,and ethaneare stripped, out of the. solventand sub- 'sequently distilling the remainder of the. ethylene andv ethane. from the strippedv solvent.

1 fJOHN A. PATTERSON.

1 REFERENCES CITED The following references are of record in the file of this patent:

I l UNITED' STATES PATENTS Number .Name ".Date

1,422,183 Curme,'Jr. 'July,1l,' 1922 1,422,184 "'Curme 'iJu1yi11,'1922 1,938,991 I "'Wulif Dec. 12.11933 2,190,025 Hull Feb; 13, 1940 2,236,966 'j Balthis et a1. ,Apr.' 1,1941 2,288,461 iKeith et al 'June30,' 1942 2,325,379 Durrum July 27, 1948 2,344,969 *Claifey, Mar. 28, 1944 2,374,104 jKirkbridge 'Apr. 17, 1945 2,374,984 Evans et al. .7 May 1,1945 2,383,547 'Hamill'et al. Aug. 28, 1945 2,407,997 Patterson; Sept. 24, 1946 12,434,796 .Hachm'uth Jan..20, 1948 32,486,543 Wen'zke -Nov. 1, 1949 2,542,520 Hibshman Feb. 20,1951 

1. A PROCESS FOR SEPARATING ETHYLENE AND ETHANE FROM A GASEOUS MIXTURE CONTAINING HYDROGEN, METHANE, ETHYLENE AND ETHANE WHICH COMPRISES SUBJECTING THE GASEOUS MIXTURE TO EXTRACTIVE DISTILLATION AT A PRESSURE OF 200 TO 300 P. S. I. IN AN EXTRACTIVE DISTILLATION ZONE IN THE PRESENCE OF A SOLVENT SELECTED FROM THE GROUP CONSISTING OF ACETONE, FURFURAL AND WATER SOLU- 